#11.2(1)
#def city_function(city,country):
#    return f"{city.title()},{country.title()}"

#11.2(2)
#def city_function(city,country,population):
#    return f"{city.title()},{country.title()}-population {population}"

#11.2(3)
def city_function(city,country,population=''):
    if population:
        return f"{city.title()},{country.title()} -population {population}"
    else:
        return f"{city.title()},{country.title()}"